1. Field of the Invention
This invention relates to printing presses, particularly to offset lithographic presses, and more particularly to a web-fed, multicolor offset lithographic press having a plurality of printing units for printing different color images on a continuous web of paper or like printable material. Still more particularly, the invention deals with such a press wherein each printing unit has at least one plate cylinder which is split in part along a plane normal to the cylinder axis into a pair of halves for independently carrying a pair of printing plates thereby concurrently to print a pair of images in transverse juxtaposition on the web. Even more particularly, the invention concerns how to drive the split plate cylinder or cylinders and associated blanket cylinder or cylinders of each printing unit.
2. Description of the Prior Art
Japanese Patent No. 2,566,895 is hereby cited as disclosing a web-fed multicolor offset press with split plate cylinders, in combination with a cylinder drive mechanism similar to the instant invention. Shown in this parent is a stack of four printing units, each of offset perfecting press design, for printing four-color images on both sides of the web as the latter travels through the successive printing units. Each printing unit comprises two split plate cylinders and two blanket cylinders. Each plate cylinder is in rolling contact with one blanket cylinder, which in turn is in rolling contact with the other blanket cylinder. The printing plates on each plate cylinder print the inked images on one blanket cylinder, from which the images are transferred or offset to the web as it passes between the two blanket cylinders. Using this blanket-to-blanket printing method, the four printing units print four-color images on both sides of the web.
The positions of the pair of halves of each plate cylinder of each printing unit are independently adjustable both axially and circumferentially of the plate cylinder with respect to the plate cylinder halves of the other printing units. Such axial and circumferential adjustment of the plate cylinder halves, together with the printing plates mounted thereon, is essential for the four-color images to be printed on the web in exact registration both transversely and longitudinally of the web.
The Japanese patent cited above suggests use of but one electric motor for driving the total of four halves of the two plate cylinders, as well as the two blanket cylinders. It also shows axial adjustments for independent axial displacement, and circumferential adjustments for independent circumferential displacement, of the plate cylinder halves.
In offset lithographic printing in general, as taught by the Japanese patent above as well as by Japanese Unexamined Patent Publication No. 61-182951, the driving torque should first be transmitted to a smaller diameter one, then to a larger diameter one, of each plate- and blanket-cylinder combination. This driving scheme is known to minimizes the adverse effects of backlashes that are unavoidably present in the drive linkages, realizing a higher degree of image registration on the web. That scheme has therefore been adopted in the prior art press in driving the two split plate cylinders and two blanket cylinders of each printing unit by one electric motor.
The arrangement of smaller diameter parts upstream of larger diameter ones in the direction of power transmission is per se desirable and acceptable. However, it gave rise to an assortment of difficulties and inconveniences when applied to the driving of the two split plate cylinders and two blanket cylinders by one motor. First, the drive linkages required too many parts and components of highly involved configurations. Such numerous parts and components demanded too much time, labor, and skill for fabrication, assemblage, and maintenance. Mechanical troubles were also just as frequent as the drive means were complex. Additionally, as the many parts of the linkages rotated at high speed and in engagement with one another, noise production posed a serious hazard to the mental health of the printing plant personnel.
Making the matter worse were the axial and circumferential adjustments that must be provided for each half of each plate cylinder in close constructional and functional association with the cylinder drive mechanisms. Designed for precise multicolor image registration both transversely and longitudinally of the web, these adjustments were themselves highly complex in construction as they should not interfere with torque transmission to the plate cylinder halves as well as to the blanket cylinders. They must, moreover, permit each plate cylinder half to be displaced independently of the other plate cylinder half, and the axial and circumferential travels of each plate cylinder half must be independent of each other. The axial and circumferential adjustments were therefore themselves extremely complex in construction, demanding much time, labor and skill for fabrication and assemblage of the constituent parts and for maintenance of the completed mechanisms.
These axial and circumferential adjustments were, furthermore, so intricately interrelated with the prior art single-motor cylinder drive mechanism that the latter was rendered even more complex in construction. Thus the single-motor drive mechanism together with the axial and circumferential adjustments was highly susceptible to trouble and malfunctioning, adding substantively to the downtime of the press.
The present invention has it as an object, in a web-fed, multicolor offset lithographic press of the kind defined, to provide a simplified, easier-of-assemblage, more trouble-free, and less noise-producing drive system for the split plate cylinder or cylinders and blanket cylinder or cylinders of each printing unit.
Another object of the invention is to attain the first recited object of the invention with a smaller diameter one or ones of the split plate cylinder or cylinders and blanket cylinder or cylinders disposed upstream of a larger diameter one or ones thereof with respect to the direction of driving torque transfer for reduction of the effects of backlashes of the drive linkages.
Another object of the invention is to associate, both functionally and constructionally, the cylinder drive system with the axial and circumferential adjustments of the plate cylinder halves without any mutual interference, and in such a manner that these adjustments too are made simpler in construction.
Briefly, the invention may be summarized as a web-fed offset lithographic press for printing multicolor images on a continuous web of paper or like material traveling through a series of printing units. Each, or at least one, of the printing units comprises a plate cylinder split into a pair of halves for separately carrying printing plates thereby concurrently to print on one side of the web a pair of images in juxtaposition transversely thereof, the pair of halves of the plate cylinder being capable of independent displacement both axially and circumferentially of the plate cylinder; and a blanket cylinder in rolling contact with both halves of the plate cylinder. Two drive motors capable of synchronous operation are provided in combination with two drive linkages. One drive linkage drivingly connects one drive motor to one of the plate cylinder halves. The other drive linkage drivingly connects the other drive motor to the other plate cylinder half and to the blanket cylinder, transmitting power first to a smaller diameter one, then to a larger diameter one, of the plate cylinder half and the blanket cylinder.
Preferably, and as in the preferred embodiment to be presented subsequently, each printing unit is of the known offset perfecting press construction, additionally comprising a second plate cylinder split into a pair of halves for concurrently printing on another side of the web a pair of images in juxtaposition transversely thereof, and a second blanket cylinder in rolling contact with both halves of the second plate cylinder and with the first recited blanket cylinder. The web has its opposite surfaces printed at one time while traveling between the first and the second blanket cylinder.
In this application the cylinder drive system comprises a third drive linkage drivingly connecting a third drive motor to one half of the second plate cylinder, and a fourth drive linkage drivingly connecting a fourth drive motor to the other half of the second plate cylinder and to the blanket cylinder. Like the second mentioned drive linkage, the fourth drive linkage transmits power first to the smaller diameter one, then to the larger diameter one, of the second plate half cylinder and the second blanket cylinder.
It is also preferred that there should be provided first and second axial adjustment means for causing axial displacement of the respective halves of the first recited plate cylinder independently of each other, and in the case of offset perfecting press construction, third and fourth axial adjustment means for causing axial displacement of the respective halves of the second plate cylinder independently of each other, with a view to fine repositioning of the pair or pairs of images transversely of the web. The drive linkages connect the drive motors to the plate cylinder halves via the axial adjustment means.
Thus, according to the invention, the halves of the plate cylinder or cylinders are individually driven from the separate motors via the separate drive linkages under synchronization control. Not only the drive linkages to the plate cylinder half or halves alone, but also those to the plate cylinder half or halves and the blanket cylinder or cylinders, are therefore much simpler in construction than the prior art in which all these components are driven from one motor. Although the invention requires four cylinder drive motors for each printing unit of offset perfecting press design, compared to one according to the prior art, this disadvantage is more than amply offset by the resulting simplicity of the drive linkages.
The independent driving of the plate cylinder halves offers the additional, but even more pronounced, advantage that the independent cylinder drive means serve not only for driving the plate cylinder or cylinders and blanket cylinder or cylinders but for circumferentially repositioning the plate cylinder halves relative to the circumferential positions of those of the other printing units in order to achieve image registration longitudinally of the web. No dedicated circumferential adjustments, such as those used heretofore, are needed. A very substantive saving is accomplished in parts and components for the driving and circumferential adjustment of the plate cylinder halves, realizing corresponding curtailment of the installation costs.
The noted simplification of the cylinder drive system and the circumferential adjustments in particular is also believed to lead to significant reduction of troubles, easier maintenance, and, in consequence, lessening of running costs. Still further the simplified cylinder drive system with the associated axial adjustments permits assemblage and maintenance by workers having ordinary skill in the art. Further yet, since the simplified drive system has fewer contacting parts, much less noise is to be produced than heretofore, with the consequent improvement of the working environment for printing plant personnel.